Over the past 20 years, the prevalence of obesity in Mexico has more than doubled among individuals across the lifespan, including even the youngest populations. Once present, obesity is difficult to treat. To halt the obesity epidemic, we need to intervene early in life before excess weight gain takes hold. An important and untapped resource to halting this obesity epidemic is the primary care provider. Primary care providers, including family physicians and nurses, are interested in combating the rise of obesity in their patients, and families trust the advice they get from their providers. The overall goal of this research is to test the feasibility and effectiveness of an innovative clinic-based intervention to promote healthy eating and activity behaviors among Mexican children aged 2-5 years at elevated risk of obesity. Our proposed intervention will build upon our work with High Five for Kids, a U.S.-based, NIH funded obesity prevention intervention that involved restructuring primary care based on the chronic care model and training clinicians to provide behavior change counseling to parents of children age 2-5 years. To achieve this goal, we will conduct a randomized controlled trial (RCT) in 10 family medical clinics of the Mexican Institute of Social Security (IMSS), a large integrated health care system that provides health care for over 45 million Mexicans. The primary aim is to assess the extent to which the intervention, compared with the usual care control condition, reduces change in body mass index over a 6-month intervention and 6-month follow-up period. We will also assess the intervention's effect on specified obesity-related behaviors and its feasibility and acceptance. The proposed study unites a multidisciplinary research team with diverse strengths; the Harvard researchers provide expertise in the epidemiology of childhood overweight in the development of innovative obesity prevention interventions, while the IMSS researchers provide expertise in experimental design and an established record of research collaboration with IMSS clinics. This research will be conducted primarily in Mexico City at IMSS in collaboration with Ricardo Prez-Cuevas, as an extension of NIH Grant No. 5R01HD050966-05, 8-22-2005 to 06-30-2010, with a planned one-year no-cost extension to 06-30-2011.